This invention relates to electron-emitting devices.
Electron-emitting devices are used in various applications such as in light-emitting devices or displays, high-frequency vacuum electronics or in applications where an electron source is needed for gas ionisation. Conventional electron-emitter devices are of a planar construction having a layers of p-type and n-type material overlying one another. When a voltage is applied across the layers, electrons are produced at the junction between the different materials. The electrons are caused to tunnel through the upper layer to its upper surface, which is exposed to vacuum where the electrons are liberated. Examples of such electron emitters are described in U.S. Pat. No. 5,202,571, GB 2322001 and GB 2322000.
It is an object of the present invention to provide an alternative electron emitter.
According to one aspect of the present invention there is provided an electron emitter comprising a region of n-type material, a region of p-type material and an interface junction between the two regions, the interface junction being exposed to vacuum for liberation of electrons directly from the junction into the vacuum.
The regions of n-type material and p-type material may be formed by a layer of one material on the other material, the interface junction being exposed at an edge of one of the layers. The p-type material is preferable formed on the layer of n-type material, an upper surface of the layer of p-type material being exposed to the vacuum and the layer of p-type material being thin enough to allow electron transmission through the layer into the vacuum in addition to liberation at the exposed junction. Alternatively, the regions of n-type material and p-type material may be provided by respective layers on a common substrate, the interface junction being formed along adjacent edges of the two regions. The edges of the layers may be inclined relative to the substrate. The region of p-type material is preferably less than approximately 1 micron thick.
The emitter may include a plurality of exposed interface junctions. The plurality of interface junctions are preferably formed by a plurality of particles of one type of material adjacent regions of the other type of material. The particles may be of p-type material and may be of both p-type material and of n-type material, the junctions being formed between particles of different types. The particles are preferably in the size range of 500 nm to 50 nm. The n-type region may be a layer on a substrate, the particles being of p-type and being located on the substrate between an edge of the n-type region and an ohmic contact.
The p-type material is preferably activated to exhibit negative electron affinity such as by treatment with a hydrogen plasma or by deposition of a low work function material. The p-type material is preferably of diamond.
According to another aspect of the present invention there is provided a method of forming an electron emitter device including the steps of providing a suspension of p-type particles in a suitable solution and using an ink-jet printing process to deposit the particles on a substrate and thereby form a plurality of electron emitter junctions.
According to a further aspect of the present invention there is provided a method of forming an electron emitter device including the steps of providing a suspension of n-type particles in a suitable solution and using an ink-jet printing process to deposit the particles on a substrate and thereby form a plurality of electron emitter junctions.
Both n-type and p-type particles may be deposited on the substrate so that junctions are formed between n-type particles and p-type particles. The p-type particles are preferably of diamond.
According to a fourth aspect of the present invention there is provided an electron emitter formed by a method according to the above other or further aspect of the present invention.
According to a fifth aspect of the present invention there is provided a display including an electron emitter according to the above one or fourth aspect of the present invention.
The display may include a plurality of electron emitters.
Electron emitter devices and a display according to the present invention, will now be described, by way of example, with reference to the accompanying drawings.